The invention relates to a process for the treatment of surfaces of highly oriented polyolefin objects. It is known to prepare highly oriented polyolefin objects, such as filamens, tapes or films from a solution of a high molecular polyolefin, see for instance U.S.-A-No. 4,344,908, U.S.-A-No.-4,411,854, U.S.-A-No.-4,422,993, U.S.-A-No.-4,430,383, U.S.-A-No.-4,436,689, U.S.-A-No.-4,668,717, GB-A-2,164,897 and EP-A-181,016. According to these references a solution of a linear polyolefin with a weight average molecular weight of at least 4.times.10.sup.5 g/mol is spun or extruded, the object obtained after spinning or extrusion is converted into a gel-object by cooling, and this gel-object is stretched at an elevated temperature. It is also known to prepare such objects from a melt of a polyolefin. See for instance U.S.-A-No.-4,525,564.
Polyolefins are nonpolar polymers that have been known for a long time and which can be, and are, used for a large number of purposes. A number of applications consist in combining polyolefins with other substances (or plastics), for example in multi-layer films or composites, or applying an adhesive, ink or paint layer or a coating to an object manufactured from a polyolefin. Use is often made of materials with a polar character in these applications. A problem in such applications is the nonpolarity of the polyolefins, on account of which it is very difficult to obtain good adhesion between the nonpolar polyolefin and materials that are more polar than the polyolefin, for example polar substances (or plastics), resins and metals.
Various solutions to this problem have been suggested, for example treating the polyolefin object with oxidizing liquids such as chromic acid (so-called etching) or subjecting it to a plasma
discharge treatment as described in EP-A-No. 62.491. However, these methods are complicated or expensive, while the strength and the stiffness of the polyolefin material are usually affected and, moreover, the adhesion is often unsatisfactory.